Radiation-sensitive emulsions and elements and their preparation



United S a s, P n e.

3,189,456 RADlATifiN-SENSETHVE EMULSEQNS AND ELE= MENTS AND TEEHR PRElARATlGN Heman Dowd Hunt, Eatontown, NJ, assignor to E. ii. du Pont de Nemours and Company, Wilmington, Del, a corporation of Delaware N Drawing. Filed June 19, 1%61, Ser. No. 117,305 2 (Iiaims. (Cl. 96-102) This invention relates to radiation-sensitive, silverhalide emulsions; to photographic elements embodying the same and to processes for making the emulsions. More particularly, it relates to such products and proc esses wherein the emulsions and elements are direct-writing, light-developable, have high speed and resolution, and have good contrast and image stability.

Radiation sensitive papers adapted for light recording, e.g., oscillographic recording, are known. These papers are commonly of the developing-out and print-out types. The developing-out type, as the name implies, requires that the exposed paper be chemically developed, fixed and washed in order to provide a stable visible image. The print-out type of paper requires no liquid development step and may or may not be stabilized and fixed. Such papers are generally much slower than those papers used in the developing-out processes and the images are unstable and have a short life. The images become masked as the background fogs or increases in density so that image detail is lost.

A third type of radiation-sensitive paper especially suitable for light-writing and oscillographic recording comprises a silver halide emulsion layer which, when exposed to a high intensity source of radiation, forms a latent image which can then be developed by exposure to diflfuse daylight or artificial light of lower intensity. Such layers are faster than print-out emulsions and re quire no chemical development. 'It is this third type of direct-writing, light-developable photographic silver halide emulsion and printing material with which the present invention is concerned.

Proposed emulsions of the third type, prior to the invention of Hunt US. application Ser. No. 814,954, filed May 22, 1959, now abandoned, in general include silver bromide emulsions which have incorporated therein, sulfur-containing compounds as halogen acceptors, e.g., thiourea and thio-semicarbazides. The background and image densities of layers comprising such emulsions, however, are not sufliciently stable to permit rapid access to or prolonged examination of the recorded images. it has also been proposed to make radiation-sensitive emulsions of the third type by introducing silver thiocyanate into a silver bromide emulsion. The sensitivity of this emulsion is greater than pure silver bromide emulsions containing halogen acceptors. However, such emulsions, after being light-developed, do not provide a stable image. Upon prolonged exposure to ordinary illumination, the background darkens quite rapidly which reduces the ratio between background and image densities. Also, where the development radiation contains a high proportion of ultraviolet light, subsequent exposure to such light (after light development) causes an increase in background density and rapid regression of the light-developed image. It is necessary to bathe the light-developed image in a liquid developing bath containing a siliver halide solvent to intensity and preserve the contrast or ratio of background to image density of the originally light-developed image. Treatment in a conventional photographic fixing bath is also'recommended.

Recently it has ben found that light-developable directwriting, radiation-sensitive elements can be made which have greatly enhanced internal latent image developability. Such elements are made by adding to a conven- 1 described in the Hunt application. This modification involves addition of at least 0.1 mole percent of a watersoluble, ionizable plumbous salt to stabilize the background. This modification constitutes the invention and subject matter of assignees copending application Hunt U.S. Ser. No. 852,190, filed Nov. 12, 1959, Patent No. 3,033,682.

As disclosed in the two copending Hun applications, the photographic elements coated with the above emulsions are quite useful in oscillographic instruments where the exposing radiation is primarily in the ultraviolet and blue regions or the spectrum. Xenon tubes and highpressure mercury arc lamps are usually used in these instruments. Speed in oscillography is measured in inches per second of a moving spot of light and is called writing speed. For the above described elements, the writing speed is of the order of about 40,000 inches per second in a dnect-writing instrument using a high-pressure mercury arc lamp.

An object of this invention is to provide new and commercially useful light-developable, direct writing, radia- 'tlOIl-SEBSlTLlVE photographic silver halide emulsions, emul sion layers and elements, e.g., papers and films, embodying such layers. Another object is to provide such products which can be exposed with visible radiation as well as ultraviolet radiation. Another object is to provide such elements which have high writing speeds. A further object is to provide a simple and efiective process for preparing such emulsions. Still further objects will be apparent from the following description of the invention.

The novel light-developable, direct-writing silver halide emulsions of this invention comprise a washed, light-sensitive colloid silver halide emulsion having an average grain size of 0.1 to 10 microns containing (1) 0.5 to mole percent of a water soluble stannous salt, (2) a sensitizing amount of an optical sensitizing dye taken from the group consisting of cyanine, pseudocyanine, 'carbocyanine and merocyanine dyes capable of extending the sensitivity of a silver bromide emulsion from the normal blue region to at least one of the green, red and infrared regions of the spectrum, and having added thereto (3) at least one water-soluble halide taken from the group consisting of lithium, sodium, potassium, calcium, .magnesium and ammonium chloride, bromide and iodide in an amount suficient to provide an excess of halide ions over that necessary initially to precipitate all of the silver ,as silver halide. In general, there should be at least a 10% excess of halide'ions present and they preferably are bromide ions. The preferred emulsions will also contain (4) 0.1 to 25 mole percent of a water-soluble inorganic plumbous salt per mole of silver. The sensitizing dye, in general, will be present in an amount from 0:1 to 0.5.millimoles per mole of silver.

According to a further aspect of the invention, the process for making the light-developable direct-writing colloid-silver halide emulsion is characterized by adding to the liquefied, washed (i.e., with water) colloid-silver halide emulsion having an average silver halide grain size in the range of 0.1 to 10 microns, the desired optical sensitizing dye, maintaining the emulsion at a temperature from 50 C. to 70 C. for a period of about 5 minutes Fatented June 15, 1965 g to remove soluble salts. 1 sion can be made by precipitating the silver halide or mix- 1 ture of silver halides in an aqueous solution containing a water-permeable organic colloid, in any conventional man- I ner. Thus, they. can be made by slowly adding'an aqueous referred to above.

addition of more of thewater-permcable colloid or of a different compatible water-permeable colloid. An aqueous solution can be used for this. purpose. The

a sensitizing dye is preferably added 'to the emulsion from a solution in anhydrous or aqueous ethanol and the stannous and plumboussalts can be added from water, ethanol,

glycerine, monethylether of ethylene glycol, or other water I miscible organic SOIVEHL' In-the case of hydrous salts,

e.g., hydrous stannous salts, they may be added in the liquefied or molten form. 7 a

The washed silver halide emulsion used in accordance with theinvention can be made by washing withwater.

A colloid silver halide emulsolution containing a water-soluble silver salt, e.g., silver L nitrate, to an aqueous solution containing (l) a watersoluble halide or a mixture of such halides, e;g., lithium, sodium, potassium, calcium, magnesium or ammonium chloride, bromide or iodide and (2) a water-permeable l organic colloid of high molecular Weight. and possessing protective colloidproperties, preferably gelatin. In making silver bromide emulsions,.it is preferable to use potassium bromide in an amount sufiicient to provide an excess. 'of 10% to 50% :or more of bromide ion over that necessary to react with the silver salt, e.g., silver nitrate.

After precipitation, ripening .is allowedto proceed to. provide the proper grain size. The emulsions may or may 1 not be digested, as desired, and additional water-permea ble colloid added to bulk up the emulsion."

Suitable stannous salts includes stannous chloride, anhydrous stannous chloride [SnCl -2H O] and stannous sulfate. vSuitable lead or plumbous salts which can be 1 used include plumbous nitrate and plumbous acetate.

The optical sensitizing dyes referred to above preferably do not contain Water-solubilizing groups in the nucleus,

. e.g., sulfonic or=carboxylic groups and their water-soluble 5 sodium, potassium, ammonium and amine salts because it is desirable to use dyes whichare readily and strongly adsorbed to the silver halide grains. The photographic emulsions obtained'in accordance with the above procedu res can be coated onto a suitable base in any of the conventional manners for coating gelatino-silver halide 'emulsions'onto paper or polymeric film base.

In processing the silver halide emulsion coated elements described above, it is only necessary after the imageforrning exposure, to expose the element to ordinary artificial room light or diffuse daylight or any actinic radiation of lower intensity than the exposinglight; f More 5. J intense radiation may be used if the element is heated durf ing this second step. Photodevelopment under 40-watt, lwhite fluorescent lights at 50 foot-candles intensity has been found to be satisfactory. Higher photographic speed is obtained by the presence of optical sensitizing dyes and greater flexibility in the selection of oscillographic light sources is possible. Theprocess of the invention is equally satisfactory when used with emulsions containing watersoluble stannous'salts alone in combination with an excess of gromide ions, which are heat-stabilized after the image exposure according to the disclosure of Hunt U.S. application Ser. No. 61,840 (U.S.P. 3,033,678) or with the addition of water-soluble plumbous salts with the stannous ;salts and an excess of bromide ions according to the di s-.

closure of Hunt application Ser. No. 852,190 (U.S.P. 7

In the process of this invention, sequence of the addi-' tion of the various constituents to the washedcolloidsilver halide emulsions is quite important. Applicant has found, which is quite surprising, that the sensitizing dye cannot be successfully added after the water-soluble stannous and plumbous salts have been added, because the latter have an adverse effecton the sensitizing action of the dye if they are added later. a

The photographic elements of this invention embody- 'ing the novel dye-sensitized, light-developable, directwriting' silver halide emulsions can be subjected togan image-forming exposure by means of radiation, the spec:

tral composition of which preferably includesradiation in the region of inherent sensitivity of the silver halide emulsion and alsoradiation in the region of extra response of said emulsion conferred by' addition of the. optical l sensitizing 'dye. The exposure time may be the same as described in the patent applications referred toabove and range from 0.01 orlessto 10,000 microseconds depending on the intensity of the exposing light.

photodevelopment. Without heat, the photodevelop ment radiation must be of less intensity than the exposing light. V

' In the detailed illustrative examples which follow, the coated elements were tested by using a Mark III Edgerton, Germenshausen and Grier, inc, electronic flash sensitomet'er similarto that'described by Wyckofi and Edgerton,

Journal of the Society of Motion Picture and Television Engineers 66, 474 (-1957). Thiszinstrument contains a xenon discharge tube as a sourceof radiation and the exposure time was 10 seconds.

a density from 0.05 to 3.05. :The latent image formed was photodeveloped by exposing the element to white light one liter of 1.5 molar solution of silver nitrate. emulsion was held for 5 minutes and there was then added is disclosed in U.S. Patent, 1,990,681.

for a period'of several minutes to obtain maximum image density. With this type of light-development, a much more stable image is obtained. Light-development by first heating and then exposing to a higher intensity light source canv result in a readable image in about one second or less, with only a slight'increase in backgrounddensity.

The presentinvention will be further illustrated by, but

' is not intended to be limited to, the following detailed examples. e

' Example I A gelatino-silver chlorobromide emulsion wasma'de. in the following manner. To an approximately 1% aqueous gelatin solution containing 1.5 moles of potassium chloride and .075 mole of hydrochloric acid there was added over a period of 25 minutes at a temperature of 140 F. The

160 mole percent of potassium bromide based on the silver. The emulsion was ripened for 40 minutesat 140 After exposure, the element is either subjected to heat and light or higher intensity or to white light of about 50 foot-candlesfor V The sensitometerwas. modulated with a /2 step tablet of 21 steps ranging in F. and cooled. The emulsion was washed by coagulation A and redispersed in the manner described in Example'l of Moede U.S. 2,772,165. The gelatin concentration was raised to approximately 6.5% during which time the temperature was raisedto and held at 130"v F. At this point, 150 milligrams of the ,dye: 5,5'-dimethyl 3,3,9-,triethyl benzselenazole carbocyanine iodide was added from a 1: 1000 methanolic solution. The preparation of this dye The emulsion was held at 130 F. for five minutes and then there was added an aqueous solution of plumbous nitrate in an amount to provide one mole percent of lead based on the silver halide. Potassium bromide was added to give an excess of 30 mole percent of bromide ions based on the silver halide. The emulsion was again held for five minutes at F. and 10 mole percent of stannous chloride was added from a 57% aqueous solution. The emulsion was held for five minutes at 130 F. and then cooled to 95 F. Various coating aids including a hardener Were added and the emulsion was coated to give a coating weight equivalent to 30 milligrams of silver nitrate per square decimeter. The coated emulsion was dried in a conventional manner. The emulsion was exposed in the sensitometer described above to white light, blue light by means of a Wratten filter, green light by means of a Wratten #61 filter, and to red light by means of a Wratten #29 filter. Under the influence of the 1O second flash exposure in the sensitorneter, the following results were obtained which are given as the number of steps made visible through the /2 step wedge. The photodevelopment step consisted of exposure for 30 minutes under 40-watt white fluorescent lights at 50 foot-candles intensity. The letters W, B, G, and R indicate white, blue, green and red, respectively. The term D indicates the density of step 21 of the wedge for a white light exposure after 30 minute photodevelopment. The term A indicates the differences between fog or background density and image density obtained through step 21 of the 2 step wedge. A control containing no sensitizing dye was also exposed for comparison.

W B G R D21 Fog A Test 17 12 8 13 51 17 34 Control 17 14 48 16 32 Example II Example I was repeated except that 150 milligrams of 3,3'-diethyl-9-methyl-benzothiazole carbocyanine p-toluene sulfonate was added in place of the dye of Example I. This dye is described by Hamer in JCS. 1928, pages 3169-3163. All operations in' the preparation, coating, drying and testing were carried out in the same manner as described in Example I with the following results.

W B G R D21 Fog A Test 18 12 12 7 .55 .21 .34 Control 17 14 .48 .16 .32

.Example 111 Example I was repeated except that in place of the optical sensitizing dye of that example there was added 150 milligrams of the dye; 5,5'-dibromo -3,3-diethyl-9- methyl benzothiazole carbocyanine p-toluene sulfonate. All other conditions and operations remained the same. The exposure results are as follows:

W B G R D21 Fog A Example IV Example I was repeated using in place of the optical sensitizing dye of that example, 150 milligrams of the dye: 5,5-9trimethyl-3,3-diethyl benzotbiazole carbocyanine iodide All other conditions and operations re- Example 1 was repeated using 150 milligrams of the dye: 5,5-diphenyl-9-methyl-3,3-diethyl benzoxazole car- 8 I bocyanine iodide. All other conditions and operations remained the same. The exposure results are as follows:

W B Gr R D21 Fog A 19 13 14 4s 17 31 17 14 4s l6 32 Example VI Example I was repeated using milligrams of the dye: 5,5'-dimethyl-3,3'-9-triethyl benzothiazole carbocyanine iodide. All other conditions and operations remained the same. The exposure results are as follows:

W i B G R D21 Fog A Test 17 12 8 9 55 20 35 Control 17 14: 48 16 32 Example VII Example I was repeated using 150 milligrams of the dye: 5,5 '-dimethyl-9-phenyl 3,3-diethyl benzothiazole carbocyanine iodide. All other conditions and operations remained the same. The exposure results are as follows:

W B G R D :1 Fog A Test 16 12 3 5 53 22 31. Control 17 14 418 l6 32 Example VH1 W D21 A Test; Control While stannous chloride can be used in aqueous solutions, the solutions tend to become cloudy although this characteristic does not appear to interfere with its activity in the system. To overcome the cloudiness the stannous chloride may be dissolved in glycerine or sorbital which provides a convenient means of adding an anticurl agent to the emulsion which is especially desirable in coatings on paper. Other stannous salts may be used such as, for example, stannous sulfate.

The optical sensitization of emulsions of this invention is not affected by the presence of relatively high quantities of stannous salts. In this respect the presence of stannous salts is not critical. This is considered to be an advantageous and novel feature because since the stannous compounds have such a profound effect on the silver halide, it would logically be assumed that its presence would interfere with tne adsorption of the sensitizing dye on the silver halide grain. This would be true if the dyes were added at the same time or after the tin and lead salts Were added. Additional suitable sensitizing dyes which can be used in place of those in the examples and modifications of the invention include the merocyanines disclosed in Kendall U.S.P. 2,272,163 and the selenopseudocyanines disclosed in Dieterle et al. U.S.P. 2,310,- 339.

Where it is desired, other halides or combinations of halides may be used to form the silver halide grains. For example, pure silver chloride, chlorobromide or iodobromide may be used. Where soluble chloride salts are used, it is desirable, because of solubility product differences, to form the silver halide grains of desired concen- In place of the gelatin binding going examples, there may be substituted other natural ,or' synthetic water-permeable organic binding agents.

tration befo're the addition of the excess bromide ions;

The operative association ofleadsalts with excess bro- -mide ions is advantageous in that the washing stepmayv be'eliminated if desired.-

Such'agents include water-soluble or -permeable poly vinyl alcohol and its'derivatives, e.g., partially hydrolyzed polyvinyl acetates, polyvinyl ethers and acetals containing a large number of extralinear CH OH-groups; hydrolyzed interpolymersof vinyl acetate and unsaturated addition polymerization compounds, for example, maleic anhydride, acrylic and methacrylic acid esters andamines and styrene. Suitable colloids of thelast mentioned type are disclosedin U.S. Patents 2,276,322, 2,276,323 and 2,397,866. The useful polyvinyl acetals include polyvinyl acetaldehyde, polyvinyl ,butyraldehyde 'and polyvinyl SO: 7 dium o-sulfobenzaldehyde. ,agents include the poly-N-vinyllactams of Bolton U.S. Patent 2,495,918.

Other. useful colloid binding These compounds include polyvinyl pyrrolidone. Nacrylamido alkyl betaines and copolyimers thereof are described in Shacklett, Patent As disclosed above, the dye-sensitized emulsions of this invention can be-coated on any suitable support, e.g., sized or unsized paper, or paper substitutes made from 'noncellulosic fibers, or a polymeric fihn composed of a cel-- -lulose ester including cellulose acetate; cellulose propionate and cellulo'seacetate/butyrate or'a superpolymer 1 such as polyvinyl chloride co vinyl acetate; a polyvinyl acetal, e.g., a formal or acetaldehyde acetal; polystyrene; polyamide, e.g., polyhexamethylene adipamide or'a polyester, e.g., polyethylene terephthalate and polyethyl I ene terephthalate/isophthalate.

cop'olymer-coated oriented flexible polyester films of Alles iet al.U'.S. Patent 2,627,088 and Alles U.S. 2,779,684 are "quite suitable supports. The various film bases may, if

The vinylidene chloride desired, contain a suitable white or other colored opacify ing agent.

An advantage of the invention is that the optical sensitization of the light-developable, direct-writing, colloid silver halide emulsion layers is not aifected bythe presence of the relatively large quantities of stannous salts. This is quite surprising and, is probably due to the fact I that the dye is added first, as stannous compounds ordinarily have a profound effect on the silver halide grain :and it would logically be assumed that its presencewould vinterfere with adsorption of the sensitizing dye on the silver halide grains.

The radiation-sensitive elements of this invention, in

. addition to being extremely convenient to use because of the elimination of Wet-processing, also offer the outstanding advantage of higher photographic speed or permits Q the use of lamps weak in blue light because of their in creased response in the infrared and visible regions ofthe spectrum. Dry processing allows the operator to see and use a print image rapidly after recording. Seismology,

electrocardiograms, photocopying, X-recording and studio agent used in the,fore-.

proof papersare fieldsin addition to oscillographywhere the novel light-sensitive elements of this invention can be used.

qlclaimz f 1. A' process for making 'light-developable, direct writing colloid-silver halide'emulsion-characterized bY' adding to the liquified, Washed colloid-silver halide emulsion having an average silver halide grain size in the range of 0.1'to 10 microns, an optical sensitizing dye selected from the group consisting of cyanine, pseudocyanine, carbocyanine and merocyanine dyes capable of extending the sensitivity of a silver bromide emulsion from the normal blue region to at least one of the green, red and infraredregions of the spectrum, maintaining the emulsion at a temperature of from 50 C. to 70 C; for a period of about 5 minutes to about 20 minutes so that the dye is thoroughly mixed and strongly adsorbed to the silver halide grains, then adding about,0.1 to 120 mole percent of a' water-soluble stannous salt per mole of silver halide and a Water-soluble halide.

2.'A process for making light-developable, directwritingcolloid-silver halide emulsion characterized by adding to the Iiquefied Washed colloid silver halide emul sion having an'average silver halide grain, size'in the range of'0.l to 10 microns, an optical'sensitizing dye selected from the group consisting of vcyan ine, pseudocyanine, carbocyanineand merocyanine dyes capable of. extend ing the sensitivity of a silver bromide emulsion from the 7 normal blue region't'o' at leastone of the green, red and infrared regions of the spectrum, maintaining the emulsion at a temperature of from 50 C. to 70 C. for a pe-L riod of about 5 minutes to about 20 minutes. so that the dye is thoroughly mixed and strongly adsorbed to the silver halide grains, then adding about 0.1 to 120 mole per- 2,005,837 j 6 351 7 2,323,187 6/43 Arens et al. 9664 2,497,876 2/ 50, Fallesen et a1 9664 2,541,472 2/51 Kendall et' el. ;96-64 2,756,148 7/56 MacWilliam 96+102 2,993,893 7/61 Hunt 96l02 X 3,033,678 5/62 Hunt 96-'94 X 3,033,682 5/62 Hunt 9694 X s 1 FOREIGN PATENTS 485,609 5/381 Great Britain.

7 OTHER REFERENCES Classification Bulletin of the U.S. Patent Ofiice No.

cent of a water-soluble stannous salt and about 0.1 to 25 V mole percent of a water-soluble plumbous salt, per mole of silverhalide, and a water-soluble halide.

References Cited by the, Examiner UNITED STATES PATENTS 422, Class 96, Photographic Chemistry, Processes and.

Materials. V V NORMAN G. TORCHIN, Primary Examiner. f

HAROLD N. BURSTEIN, Examiner. 

1. A PROCESS FOR MAKING LIGHT-DEVELOPABLE, DIRECTWRITING COLLOID-SILVER HALIDE EMULSION CHARACTERIZED BY ADDING TO THE LIQUIFIED, WASHED COLLOID-SILVER HALIDE EMULSION HAVING AN AVERAGE SILVER HALIDE GRAIN SIZE IN THE RANGE OF 0.1 TO 10 MICRONS, AN OPTICAL SENSITIZING DYE SELECTED FROM THE GROUP CONSISTING OF CYANINE, PSEUDOCYANINE, CARBOCYANINE AND MEROCYANINE DYES CAPABLE OF EXTENDING THE SENSITIVITY OF A SILVER BROMIDE EMULSION FROM THE NORMAL BLUE REGION TO AT LEAST ONE OF THE GREEN, RED AND INFRARED REGIONS OF THE SPECTRUM, MAINTAINING THE EMULSION AT A TEMPERATURE OF FROM 50*C. TO 70*C. FOR A PERIOD OF ABOUT 5 MINUTES TO ABOUT 20 MINUTES SO THAT THE DYE IS THOROUGHLY MIXED AND STRONGLY ADSORBED TO THE SILVER HALIDE GRAINS, THEN ADDING ABOUT 0.1 TO 120 MOLE PERCENT OF A WATER-SOLUBLE STANNOUS SALT PER MOLE OF SILVER HALIDE AND A WATER-SOLUBLE HALIDE. 